Method and apparatus for treating molten metal with gas



Jan. 12, 1937. A. E. HALL 2,067,394

METHOD AND APPARATUS FOR TREATING MOLTEN METAL WITH GAS Filed Dec. 20,1935 2 Sheets-Sheet 1 A. E. HALL Jan. 12, 1937.

METHOD AND APPARATUS FOR TREATING MOLTEN METAL WITH GAS Filed Dec. 20,1933 2 Sheets-Sheet 2 .Other features of the invention consist in thetented Jan. l2, 1%3'7 if j:

METHOD APPARATUS FOR TREATING MOLTEN METAL WI GAS Application December2t), 1933, Serial No. 703,236

. 19 Claims.

The present invention relates to a method and apparatus for treatingmolten metal with a gas, designed and adapted more particularly for thetreatment of molten lead with chlorine gas for the purpose of removingzinc, as, for example, the zinc left in the lead from the desilvering bythe Parkes process.

The principal object of the present invention is to provide a method andapparatus whereby impurities may be removed from a molten metal by meansof a gaseous reagent in an expeditious, eflicient, and economicalmanner, as, for example, zinc from desilvered lead by the use ofchlorine gas, without loss or escape of free chlorine into the air, ordestructive corrosion of the apparatus, or the necessity of a separatereaction chamber or tank where the chlorine may bebrought intoassociation with a relatively ,smallamount of lead separate and apartfrom the mass or main body of the molten metal to be treated. Anotherobject of the present' invention is to provide for the continuous andautomatic collection and discharge from the molten metal of certainofthe products of the reaction, such for example, as the liquid zincchloride when desilvered lead is treated with chlorine, as fast asproduced by the reaction.

A further object is to provide for the absorption of heat generated bythe reaction and the application of such heat to the liquid or gaseousreagent for the purpose of supplying the heat required for vaporizationand expansion.

With these and other objects in view as will be apparent to thoseskilled in the art, the present invention consists in the method andapparatus wherein the gaseous reagent is discharged into the mass ofmolten metal while the latter is caused to circulate within itscontainer or receptacle, the gas preferably being discharged into adownwardly flowing stream of metal.

A further feature of theinvention consists in the use of a. mechanicalstirrer, such for example as a rotating screw, positioned adjacent thepoint of discharge of the gas for the purpose of circulating the metaland distributing the gas.

Still another feature consists in the use of acollector submergedbeneath the surface of the molten metal, for collecting such products ofthe reaction as tend to rise toward the surface of the metal, forexample, the zinc chloride following the treatment of lead withchlorine, and disthe same in a continuous stream over the edge of thecontainer under the action of the weight of the metal above thecollector.

use of a water cooler for absorbing excess heat from the reaction, of aheating coil with suitable connections for causing the heated water orsteam to heat the gas supply, and of a gas discharge pipe or nozzlecomprising a tube of non- 5 corrosive material, such as glass, enclosedwithin a protective metal pipe with asbestos or other suitable packingbetween to protect the glass tube from excessive heat or jar.

Other features of the invention will be pointed 10 out in the followingspecification.

In the accompanying drawings which illustrate what is now considered tobe the preferred form of the apparatus embodying and practicing theenlarged scale of the gas discharge nozzle or 25 pipe.

The apparatus shown in the drawings comprises, briefly an openhemispherical container or kettle for the molten lead, with a dischargenozzle or pipe for discharging. the chlorine gas 3g from a tank intoapproximately the center of the mass of molten metal. Mounted upon a.girder framework above the kettle is a motordriven stirrer comprising avertical screw nornially submerged in the molten metal adjacent thepoint of gas discharge. The girder. framework also carries beneath it acircular or annular collector, normally held submerged in the moltenmetal. A cooling coil connected with a water supply is alsosubmerged inthe molten metal 40 above the collector, and the hot water or steam fromthe coil is conducted to a heating coil built into the tank car forheating the liquid chlorine.

Referring to Fig. 1, the container or kettle 6 is of the usual typeemployed for the treatment of molten metal, being hemispherical in shapeand made of steel, with a supporting lip or beading 8 at its edge.Normally resting upon the rim of the kettle, but adapted to be raisedand re- 50 moved therefrom, as by a lifting crane, is a framework madeup of a lower pair of horizontal girders l0, an upper series ofcross-girders l2 secured tothe lower pair at right angles, and diagonalmembers It attached at their lower inner ends to a plate I6 having anopening I81 to receive the hook of a lifting crane.

Mounted upon this framework is the stirrer or circulating unitcomprising a screw 22 on the lower end of the vertical shaft 24, drivenby direct connected motor 26 mounted upon two short girder sections 28.

With these parts in operating position, as shown in Fig. 1, the screw orstirrer is positioned approximately at the center of the mass of moltenmetal, and when driven by its motor creates and maintains a continuouscirculation of the metal, with a downwardly flowing stream in the middleof the 'kettle and upwardly flowing streams at the sides.

Preferably a guiding sleeve 30, slightly tapering and open at both ends,is positioned around the screw, extending slightly above the top thereofandterminating a short distance above its bottom, for directing and.controlling more definitely the circulation of the metal within thekettle, as is common in this general type of stirrer or circulatingdevice.

Chlorine gas is delivered directly into the mass of molten metal throughthe discharge pipe or nozzle 34, from a suitable source of supply, such,for example, as the tank car 36, through the connecting pipe 38. Thenozzle 34 is positioned close to the top of the stirrer or screw 22 todischarge its gas downwardly into the downwardly descending and more orless turbulent stream of molten lead, and so close to the screw itselfas to cause the latter to effect an intimate association of the gas andlead whereby a rapid and complete reaction between the zinc and gas isassured.

The discharge nozzle or pipe 34 is preferably formed as shown in theenlarged detail in Fig. 4, with an inner tube 40 of pyrex glasssurrounded by a wrought iron tube 42 with end cap 44. A packing 46 ofasbestos or other suitable heat resisting material, is inserted betweenthe pyrex glass tube and the protective metal tube to protect the pyrexfrom the heat of the lead and to cushion it from jars or vibration. Asection of rubber hose or tubing 48 provides a yielding co nectionbetween the discharge nozzle and the metal pipe 38 leading from thesource of supply.

As the gas reacts with the molten metal, and more particularly with thezinc contained therein to form zinc chloride, the latter product, beingof less specific gravity than the molten metal, rises, but before it canreach the surface of the molten mass is intercepted bythe collectorindicated generally at 50. This comprises a circular annular top 52having depending inner and outer' marginal walls 54 and 56. Thecollector is supported a short distance below the surface of the moltenmetal, as shown in Figs. 1 and 2, by means of long bolts 58 extendingfrom the cross girders 12 into the top of the collector adjacent itsouter margin. An outlet or discharge duct is provided for the collectorconsisting of an upwardly extending passage 60 at one side thereof, witha slightly descending spout 62 projecting beyond the rim of the kettleto discharge the molten zinc chloride in a continuous stream into thereceptacle or kettle 64.

In order to facilitate the collection and discharge of the zincchloride, thetwo halves of the annular top of the collector are slightlyinclined upwardly towards each other, as shown in Fig. 1, while at thesame time the collector as a whole is inclined upwardly toward thedischarge, as

shown in Fig. 2. Thus the liquid zinc chloride, as it rises through themolten mass of metal, is intercepted by the collector and directedtoward the discharge, all under the influence of the weight of themolten metal lying above the collector. This automatic collection anddischarge of the zinc chloride will continue so long as chlorine isdischarged into the mass of lead and there remains any appreciableamount of zinc with which it may react.

Due to the agitation of the molten metal, there is a tendency for thelevel of the zinc chloride to rise and fall at the discharge, and inorder to avoid or limit such variations in level, a baflie plate 66 hasbeen positioned immediately beneath the discharge passage 60.

The reaction of the chlorine with the zinc in the molten metal generatesheat in excess of that required to maintain the metal in proper moltencondition, and in order to abstract and withdraw such excess heat acooling coil has been provided which is connected with a water supply.Preferably this cooling unit is mounted on the top of the collector andin close proximity thereto so that it may have a cooling effect upon thezinc chloride as well as upon the molten metal. As shown in the drawingsthe cooling coil 68 is submerged in the molten lead and positioned closeto the top of the collector, being connected with the water supply bythe water pipe 10. The hot water or steam generated by the heat of themolten material will be discharged through the pipe 14, either to wastethrough the connection 18, or through a heating coil to heat the supplyof chlorine. Preferably the chlorine supply will be in the form ofliquid chlorine delivered from a tank car 36, as shown in Fig. 1. Thesecars are constructed with inner and outer shells 82 and 84 respectively,with a filling of heat insulating material between. At the. bottom ofthe tank car between the shells and imbedded in the insulating material.is a. series of heating pipes 88 with inlet and outlet connections 90and 92. By means of the connection 94 the hot water or steam from thecooling coil 68 will be passed through the heating coil of the tank carand discharged to waste at 96, the heat of reaction thus supplying theheat necessary to vaporize and heat the chlorine.

If sufficient heat is not available from the reaction properly to heatthe chlorine, as, for example, in the winter months when atmospherictemperatures are low, a source of live steam supply may be provided asat 98, which, through suitable valved connections, may be passed throughthe heating coil in the tank car while the heated water or steam fromthe cooling coil in the kettle is discharged to waste at 18.

Preferably the water cooling coil 68 is connected to the Water supplyand discharge piping with rubber hose, as shown at I00, so that the coilmay be disconnected from the water supply in order to permit the coil tobe raised with the collector and the other parts when the framework islifted from the kettle.-

Similarly, provision is made for disconnecting the gas dischargepipe bymeans of the rubber hose I04. In practicing the process by the use ofthe above described apparatus, the kettle will be filled with the moltenmetal to be treated, as for example, following the Parkes process wheresilver has been removed by the use of zinc, leaving the zinc in thelead.

If the superposed mechanism has been removed for the p rp e offacilitating charging of the kettle, the mechanism will be replaced bythe crane, with the screw, collector and coil submerged in the moltenmetal. The gas discharge pipe is next inserted, being passed downwardlythrough the annular opening in the collector and secured in positionwith its discharge end adjacent the top of the screw. The motor isv nowset in operation to start the circulation of the molten lead, and assoon as this is accomplished, the flow of chlorine gas from the tank caror, other source of supply is started. The amounts to be admitted mustbe no more than can react with, and be absorbed by, the molten metal. Iffree chlorine appears at the surface of the molten metal, it is evidentthat the gas is being supplied at too fast a rate and must be cut down.

By reason of the circulation set up in the mass of molten metal and thedownward discharge of the gas into the downwardly moving stream of metalat a point adjacent the rapidly rotating screw, the reaction between thegas and zinc is relatively rapid and the chlorine may be fed into themass of molten metal at a relatively high rate. For example, with akettle approximately fourteen feet in diameter, containing two hundredand thirty-five tons of molten metal, and with a screw rotating slightlyless than twelve hundred R. P; M. and absorb about twenty horse power,the chlorine may be fed at a rate of from live to six pounds of gas perminute without free chlorine appearing on the surface.

As the reaction proceeds and heat is developed, water is passed throughthe cooling coil at a rate controlled by the water supply valve, andproper to maintain a constant temperature of about 670 F.

The heated water or steam coming from the coil may be conducted to thehea'tingcoil in the tank, or if by reason of weather conditions orotherwise this does not supply sufiicient heat for vaporization, thecooled water may be discharged to waste and live steam from somesuitable source passed through the heating coil in the car to vaporizethe liquid chlorine.

The chlorine reacts with the zinc to form zinc chloride according .tothe general formula This gives zinc chloride in liquid form which,because of its specific gravity relatively to the molten metal, risesthrough the latter until it is intercepted by the collector. Theinclination of the top of thecollector and the pressure of the metalabove the collector causes the zinc chloride to fiow to the dischargewhere it rises and flows over the rim of the kettle into the adjacentcollecting kettle.

So long as chlorine continues to be supplied, and there remains anysubstantial amount of zinc, the reaction will continue and liquid zincchloride will be constantly and automatically col-= lected anddischarged. The completion of the reaction will be indicated by thechange in the In the commercial use of the present invention, the zinccontent in the treated lead will be reduced to .005%. An even lowercontent could be secured if desirable or necessary by continuing theprocess under carefully controlled conditions, but inasmuch as furthertreatment of the lead is required for the removal of other impurities,which treatment also removes the remaining small amounts of zinc, it isordinarily not commercially profitable to carry the process beyond thatrequired for the .005% zinc content.

Corrosion is reduced to a minimum through the delivery of chlorine gasinto the mass of molten metal, so that the reaction take place and thechlorine is absorbed in the zinc while it is still surrounded by aprotective mass of lead. The location of the gas delivery nozzle,preferably slightly to one side of the stirrer or screw as shown in thedrawings, insures continuous contact of the screw with only the moltenmetal, thus protecting it from direct contact with, and corrosion by,the chlorine gas.

The maintenance of circulation of the molten metal in distinctdownwardly and upwardly flowing currents not only facilitates thereaction by bringing the gas into more intimate mixture with the metal,but by reason of the discharge of the gas in the downwardly flowingstream, tends to prolong the time appreciably for the reaction andreduces the tendency of free chlorine to rise to the surface. Theupwardly flowing currents also expedite the rising movement of the zincchloride and its collection by, and discharge from, the collector.

While the present process and apparatus have been described inconnection with the treatment of lead with chlorine gasfor the purposeof removing zinc, it is to be understood that the invention is notlimited to such materials or use but may be employed with othermaterials or metals or gas having the proper reactions with respect toone another. 7

Having thus described the invention, what is claimed is:

1. The method of treating molten metal with a gas which consists incausing the metalto circulate in downwardly and upwardly flowingstreams, discharging the gas into the downwardly flowing stream, andsegregating from the upwardly flowing stream and beneath the surface ofthe molten metal the products of the reaction. 4

2. The method of treating molten metal with a gas which comprisessegregating beneath the surface of the metal the products of thereaction which tend to rise to the surface of the metal, dischargingsuch products from beneath the surface of the metal, and abstractingheat from the molten metal adjacent the point of segregation.

3. Apparatus for treating molten metal with gas comprising a containerfor holding a mass of molten metal, means for bringing gas from a sourceof supply into contact with the molten metal, and, a submerged collectorbeneath the surface of the molten metal to collect the products ofreaction which tend to rise to the surface of the metal.

4. Apparatus for treating molten metal with gas comprising a containerfor holding the molten metal, means for bringing gas from a source ofsupply into contact with molten metal, and a submerged collector beneaththe surface of the molten metal to collect the products of reactionwhich tend to rise to the surface of the metal.

the collector having discharging means for conducting the collectedproducts upwardly and laterally over the edge of the container under theaction of the weight of the molten metal overlying the collector. 7

5. Apparatus for treating molten metal with gas comprising acontainerfor the molten metal, means for bringing gas from a source ofsupply into contact with the molten metal and a submerged collectorbeneath the surface of the molten metal to collect the products ofreaction which tend to rise to the surface, the collector having a ductfor conducting the collected products upwardly and laterally, and.abaflie :adjacent the inner opening of the discharge duct.

6. Apparatus for treating molten metal with gas comprising a containerfor holding the molten metal, a source of supply of liquefied gas, meansfor bringing the gas into contact with the molten metal, and means fortransferring heat from the molten metal adjacent the collected productsto the liquefied gas supply.

7. Apparatus for treating molten metal with gas comprising a containerfor holding the molten metal, a source of liquefiedgas supply, means forbringing the gas into contact with the molten metal, a cooling coil inthe molten metal for absorbing heat therefrom, a heating coil forheating the liquefied gas, and connections between the cooling andheating coils whereby heat may be absorbed from the molten metal anddelivered to the liquefied gas.

8. Apparatus for treating molten metal wit gas comprising a containerfor holding the molten metal, a gas pipe for bringing gas from thesource of supply into contact with the molten metal, power-driven meansfor causing the metal to circulate inthe container, a collector forcollecting the products of reaction which tend to rise to the surface ofthe metal, and a support, separable and removable from the container,for commonly supporting said powerdriven means and the collector withthe collector normally held submerged beneath the surface of the moltenmetal.

9. Apparatus for treating molten metal with gas comprising a containerfor holding a mass of molten metal, the container being'circula'r incross-section, an annular collector having a central opening and withits marginal edge spaced inwardly from the container, a vertical shaftextending downwardly through a central opening in the collector, a screwmounted thereon for causing circulation ofthe metal, means for drivingthe shaft and screw, and a gas pipe extending downwardly through theaxial opening of the collector for delivering gas from the source ofsupply into the molten metal.

10. The method of using a liquefied gas for the treatment of moltenmetal which consists in abstracting heat from the molten metal; applyingsuch abstracted heat to the liquefied gas to vaporize the same, andthereafter bringing the gas into contact with the metal.

11. That step in the method of treating molten metal with a reagentwhich consists in segregating beneath the surface of the metal theproducts of reaction which tend to rise to the surface. I

12. That step in the method of treating molten metal with a reagentwhich consists in segregating beneath the surface of the metal, theproducts of reaction which tend to rise to the surface, and incontinuously withdrawing such segregated products. 4

13. The method of treating molten metal with a reagent which consists inintimately associating the metal and reagent to cause reaction therebetween and thereby to form a mixture of the metal and the products ofsuclr'reaction and segregating beneath the surface of the metal theproducts which tend to rise to the surface.

14. That step in the method of treating molten metal with a gas whichconsists in segregating beneath the surface of the metal the products ofthe reaction which tend to rise to the surface of the metal, and bymeansof the weight of the metal above the segregated productsdischarging said products above the level of the surface of the metal.

15. Apparatus for treating molten metal with gas comprising a containerfor holding a mass of molten metal, means for causing the molten metalto circulate within the container, a gas pipe for delivering the gasfrom a source of supply into the metal, and means for segregating'beneath the surface of the metal the products of reaction and forcontinuously discharging from beneath said surface the segregatedproducts.

16. Apparatus for treating molten metal with gas comprising a containerfor holding a mass of molten metal, the container being of substantiallyhemispherical shape, means for imparting a downward fiow to the gnetaladjacent the vertical axis of the container and an upward fiow adjacentthe container wall, a gas pipe for discharging gas from a source ofsupply into the downwardly flowing stream of metal, and an annularcollector for collecting the products of the reaction which tend to riseto the surface of the metal adjacent the container wall.

17. Apparatus for treating molten metal with gas comprising a containerfor holding the molten metal,.means for bringing 'gasfrom a source ofsupply into contact with the molten metal, a collector submerged in themolten metal and exposed to the heat thereof for collecting the productsof reaction, and a cooling coil submerged in the molten metal adjacentthe collector for continuously absorbing heat therefrom to preventoverheating of the products of reaction.

18. The method of treating molten metal with a reagent which consists inintimately associating the metal and reagent to cause reactiontherebetween to form a molten mixture of the metal and the product ofsuch reaction, segregating the products of reaction in molten formbeneath the surface of the metal, and discharging the segregated productwhile still in molten form from beneath the surface of the metal and ata level above the surface of the metal.

19. The method of treating molten lead with chlorine gas to'remove zincwhich consists in introducing chlorine ,into the molten lead to formzinc chloride, collecting the chloride in liquid form beneath thesurface of the molten lead and discharging the liquid chloride frombeneath the surface of the lead.

